1. Field of the Invention
It has been estimated that entomopathogens, mainly Bacillus thuringiensis (B.t.), will reach a $100,000,000 market by 1992, approximately 90% of which will be sold as sprayable formulated material. Effectiveness of spray formulations is dependent on attractiveness to target pest insects and retention of pathogenic activity. This invention relates to a novel spray formulation, based on a renewable resource, which satisfies these criteria.
2. Description of the Prior Art
The use of starch has many attractive properties for biocontrol agent encapsulation. First, it is inert and will not alter resting stages of most living organisms; second, particulate or liquid UV-screening agents are easily added; third, its major component is amylopectin which is readily digested by most phytophagous pests possessing .alpha.-amylase enzymes [G. M. Chippendale et al., J. Insect Physiol. 20: 751-759 (1974); K. Nishide et al., J. Fac. Agric. Tottori Univ. 11: 12-22 (1976)]; and fourth, it is abundant and inexpensive compared to most other materials currently used in encapsulation [B. S. Shasha, In Controlled Release Technologies: Methods, Theory, and Applications, Vol. 2, A. F. Kydoniens (ed.), CRC Press, Inc., Boca Raton, Fla.].
Recently, Dunkle et al. [Environ. Entomol. 17: 120-126 (1988) and U.S. patent application Ser. No. 07/72,205 filed on July 10, 1987, now U.S. Pat. No. 4,859,377] prepared a granular formulation of B.t. encapsulated within a starch matrix. The advantage of this method over existing formulations is that it allows incorporation of various additives such as sunlight protectors to prevent solar inactivation and feeding stimulants to increase palatability and thereby reduce the amount of active ingredient necessary for control. Trimnell et al. [J. Controlled Release 7: 263-268 (1988)] have reported a sprayable herbicide formulation utilizing pregelatinized corn starch and flour. These sprays give a thin film of the formulation on plant leaves which autoencapsulates (encapsulates the active agent in situ) upon drying and thereby allows sustained release of active ingredient. However, within 2-3 days after application, these films peel away from the plant leaves. In general, sprayable formulations of B.t. lose activity within 2-4 days following application to plant foliage in the field [Morris, Can. Ent. 115: 1215-1227 (1983); Beegle et al., Environ. Entomol. 10: 400-401 (1981); Leong et al., Environ. Entomol. 9: 593-599 (1980)].